A radio frequency filter having a cavity structure generally includes a plurality of accommodation spaces having a rectangular parallelepiped shape or the like, that is, a plurality of cavities through a metallic housing, and a dielectric resonance (DR) element or a resonance element having a metallic resonance rod is provided in the cavities to generate resonance of high frequency waves. In the radio frequency filter having the cavity structure, a cover for shielding an opened surface of the cavity structure is provided at an upper portion of the cavity structure, and a plurality of tuning screws and nuts for fixing the tuning screws are installed in the cover as a tuning structure for tuning filtering characteristics of the radio frequency filter. An example of a radio frequency filter having a cavity structure is disclosed in Korean Application Publication No. 10-2004-100084 (entitled “Radio Frequency Filter” and published on Dec. 2, 2004; inventors: Jonggyu Park, Sangsik Park, and Seungtaek Jeong) filed by the present applicant.
The radio frequency filter having a cavity structure is used for processing of a radio signals transmitted and received in a radio communication system, and it is applied to a base station or a relay in a mobile communication system.
Meanwhile, in the base station or the relay of the mobile communication system, the base station body apparatuses are installed on the ground, as compared with antenna apparatuses (generally, having a large volume and a heavy weight) installed at a column located at an elevation above the ground, and the antenna apparatus and the body apparatuses are currently connected through cables. However, this installation method causes a loss problem due to connections of cables between the antenna apparatus and the body apparatuses and an installation space problem of the body apparatus. Accordingly, as equipment has gradually become lightweight and miniaturized recently, the body apparatuses (or at least some modules) are disposed in a column for installation of antenna apparatuses to be connected to the antenna apparatus or to be included in the antenna apparatus.
Thus, when a radio frequency filter is applied to a base station or a relay of a mobile communication system, being small-scale and lightweight are more important considerations.
However, because a radio frequency filter having a cavity structure includes a resonance element in a housing and basically should have a coupling structure between a cover and a housing, there is a limit as to how small-scale and lightweight the radio frequency filter can be. Further, the coupling structure for a plurality of tuning screws and fixing nuts acts as an important restriction in how lightweight and small-scale of a radio frequency filter is.